Small angle x-ray scattering is a specialized area within the more general field of x-ray scattering analysis. Unlike the more general wide-angle scattering systems, small angle systems measure phenomena that are observed within angles of just a few degrees from the primary x-ray beam. Thus, such systems may be used to provide structural information on the order of approximately one to one hundred nanometers. This allows characterization of a variety of materials that are not measurable using a wide angle system. However, small angle systems must also face a number of additional problems due to the small angle measurements.
In a small angle x-ray scattering system, the distance between the sample being examined and the x-ray detector is typically much longer than that of a wide angle system. Because of the small angular deviation from the main x-ray beam, it is necessary to have this additional length to allow adequate resolution at the x-ray detector. This, of course, increases the noise factor of the system, as the scattered x-rays have an increased opportunity to interact with ambient gas molecules. For this reason, small angle systems typically use an evacuated beampath between the sample and the detector to reduce the ambient gas density. In addition, such systems often make use of x-ray collimating apparatus located between the x-ray source and the sample. The collimator helps to reduce the incidence of parasitic capacitance, and the primary beampath within which the collimator is located may also be evacuated to reduce the presence of ambient gas molecules.